If I look up tube data for 6L6 tubes, it says it's a Beam Power Tetrode. Tube data for a 6CL6 tube says it's a vacuum pentode for power output.
I'm confused as to why the spud amplifier doesn't need a driver tube? It seems that a smaller output tube would need a driver tube.
I'm confused as to why the spud amplifier doesn't need a driver tube? It seems that a smaller output tube would need a driver tube.
Spud amps are by definition a one tube design, and a tube that does not require a driver would be chosen. The intended power level is typically a watt or less.
The 5842/417A makes a great 500mW spud amplifier for example.
Some high transconductance pentodes make good spud amplifiers as well particularly if triode connected.
The 5842/417A makes a great 500mW spud amplifier for example.
Some high transconductance pentodes make good spud amplifiers as well particularly if triode connected.
A pseudo "spud" is possible too. The 6BM8/ECL82 combines a triode and a small power pentode in a single envelope.
PRR- Okay... that makes sense.
That's also why I have to use a preamp with a spud amp.
Thank you!
That's also why I have to use a preamp with a spud amp.
Thank you!
As a random counter-example: a 6AU6 (super-common FM radio tube) can accept a bit over 1V and deliver a whopping 1/3rd Watt in 15k-25k load. Like attached but without that first stage (guitar preamp). Being a naked pentode, damping is nil and THD @ 0.3W may be many %. But hey, one tube from most modern sources to a hot loudspeaker.
For a bit more power (over a Watt), 12FX5/60FX5 is a sweet thing and still underappreciated. And still a nasty naked pentode.
There are better choices for people with money. 417A was Bell Tel's hot VHF repeater and can do good work at audio.
For a bit more power (over a Watt), 12FX5/60FX5 is a sweet thing and still underappreciated. And still a nasty naked pentode.
There are better choices for people with money. 417A was Bell Tel's hot VHF repeater and can do good work at audio.
Yes, the 5842/417A makes a great single stage power amplifier with a very efficient speaker and a good output transformer.
Other candidates would be the Russian 6N6P - you can do stereo with a single one.
D3A triode connected would be another, and you might get an entire 1 watt out of one and maybe 2W with pentode connection and there might be enough gain for some negative feedback.
I suspect that many of the video power amplifier tubes discussed here on diyA would also make good spuds.
Other candidates would be the Russian 6N6P - you can do stereo with a single one.
D3A triode connected would be another, and you might get an entire 1 watt out of one and maybe 2W with pentode connection and there might be enough gain for some negative feedback.
I suspect that many of the video power amplifier tubes discussed here on diyA would also make good spuds.
Member
Joined 2009
Paid Member
As said, you want a tube with high enough gain, most power output triodes have a low mu, so you will be looking at tetrodes and pentodes, picking a tradeoff between power and linearity.
Yukon Gold - a spud amp
Yukon Gold - a spud amp
6GF7 and 6FM7 too. Double triodes, small and large.
6GE8 is an unusual one.
Small pentode and big triode.
6GE8 is an unusual one.
Small pentode and big triode.
